Semi-conductive element



Jan. 9, 1962 A. J. RAKOWSKI ETAL 3,016,506

SEMI-CONDUCTIVE ELEMENT Filed Feb. 1, 1960 ATTORNEY Fatenteel Jan. 9,lQiiZ 3,016,506 SEMLQONDUTHVE ELEMENT Alexander ph Plalrewslri, Towaeo,.l'ames Prollins, Newark, and .l'ohn Conrad Zenobia, Sin, Helleville,NJL, assignors to Specialties Development @orporation, llelleviile, NJL,a. corporation or New .lersey Filed Feb. 1, 1960, Ser. No. 5,952 1(Ilaim. (Cl. 333 212) The present invention relates to semi-conductiveelements such as thermistors, and, more particularly, to the compositionof the body of resistance material and the terminal wires for the body.

Previously, it has been found that such elements having desirablevoltage insensitivity characteristics can be reproduced with predictableresistance values by placing a resistance material on platinum terminalwires. With the increased demand and uses for thermistor elements, it isdesirable to reduce the cost thereof as greatly as possible. Whilecertain improvements have been made in that direction, the relativelyhigh cost of platinum wires has hindered further reduction in costs.

In an attempt to use less expensive terminal wires, such as wires formedof an alloy sold by The International Nickel Company, Inc., under thetrademark lnconel and consisting essentially of between about 6% andabout 17% by weight of iron, between about 11% and about 18% by weightof chromium and the balance nickel at a minimum of 70% by weight, it wasfound that the resistance material became voltage sensitive to theextent that it did not provide a satisfactory tremistor elements where achange in its resistance in excess of about 20% could not be tolerated.

Accordingly, an object of the present invention is to provide aresistance material which is sufficiently voltage insensitive to enablethe same to be used with wires much less expensive than platinum wiresand produce a satisfactory thermistor element.

Another object is to accomplish the foregoing in a simple, practical andeconomical manner.

Other and further objects of the invention will be obvious upon anunderstanding of the illustrative embodiment about to be described, orwill be indicated in the appended claim, and various advantages notreferred to herein will occur to one skilled in the art upon employmentof the invention in practice. I

In accordance with the present invention, it has been found theforegoing objects can be accomplished by producing a semi-conductor suchas a thermistor element comprising a body formed of a resistancematerial consisting essentially of between about 50% and about 80% byweight of manganese dioxide and between about 50% and about 20% byweight of cobaltic oxide; and spaced parallel conductive terminal wiresformed of Inconel.

In the drawing, the single figure is a greatly enlarged longitudinalsectional view of a semi-conductor such as a thermistor elementembodying the present invention.

Referring to the drawing in detail, the element shown by Way of examplecomprises a cylindrical body or bead 10 having a. pair of spaced apartparallel terminal wires 11 embedded therein. This element has thefollowing dimensions:

in. Body length 0.0625 Body diameter 0.0625 'Wire diameter 0.0100 Spacebetween wires 0.0100

Suchelements are adapted to be used in networks with a potential ofabout one volt normally applied thereto.

2 EXAMPLE I An element having the foregoing dimensions was con-'structed by forming the body 10 of thoroughly admixed line particlesconsisting essentially of 75% by weight of manganese dioxide and 25% byweight cobaltic oxide and by embedding wires ll therein formed of analloy consisting essentially of 75% by weight nickel, 15% by weightchromium and by weight iron. The body 10 was fired to adhere the sameonto the wires.

The element was tested by applying measured potentials only for a shortduration to prevent appreciable self-heating effects, and measuring theresistance of the element with a bridge or a null detector.

The following readings were taken:

Table I Potential Percent Resist nce Percent Test N o. In Volts ChangeIn In K Ohms Change In Potential Resistance 0. 3 70 295 plus 3.2. 0.6 40293 plus 2.5. 1. 0 286 1. 5 50 280 minus 2.1. 2. 2 120 271 minus 5.2.3.0 200 256 minus 10.5. 4. 5 350 236 minus 17.5. 6.0 500 225 minus 21.

EXAMPLE II For comparative purposes, an element was similarlyconstructed by forming the body of a mixture consisting essentially of90% by weight of manganese oxide and 10% by weight of cupric oxide andembedding platinum wires therein. The element was similarly tested andthe following readings were taken:

Table II Potential Percent Resistance Percent Test No. In Volts ChangeIn In K Ohms Change In Potential Resistance 1..- 0. 3 70 20. 5 plus 1.4.2 0.6 40 29. 3 plus 0.7.

1.0 29.1 1. 5 29.0 minus 0.4. 2. 2 120 28. 8 minus 1.0. 3.0 200 28. 5minus 2.1. a. 5 350 27. 9 minus 4.1. 6.0 500 27. 5 minus 5.5.

These readings indicate that the element in accordance 50 with thepresent invention compares favorably with a manganese dtoxide-cupricoxide body on platinum wires where about a 20% change in resistance canbe tolerated when the normal voltage increases about 500%.

EXAMPLE in Another element was similarly constructed by forming the bodyof a mixture of the material used in Example H and embedding wirestherein formed of the same alloy used in Example I. This element wassimilarly tested and the following readings were taken:

with Example 111 is so voltage sensitive that its resistance decreasesabout 20% when the normal voltage increases only 200%.

Further cursory tests were made with materials respectively consistingessentially of 50% by weight of manganese dioxide and 50% by weight ofcobaltic oxide; and 80% by weight of manganese dioxide and 20% by weightof cobaltic oxide. it was found that elements having a body. of suchcompositions and lncone wire embedded therein were sufficicntly voltageinsensitive to enable the same to be used as thermistors.

Itwas further found that the compositions of the higher eobaltie oxidecontent exhibited greater voltage insensitivity than those of the lowercobaltic oxide content. However, the bodies formed of compositionshaving a 20% to 30% by weight cobal-tic oxide content have betterstructural characteristics.

The expressionfivoltage insensitivity and expressions of similar contextmean that the resistance of the body material does not materiallyincrease or decrease as the voltage applied across the terminal wiresrespectively decreases or increases. This effect is independent ofchanges in resistance due to the thermal coefiieient of resistivity ofthe element.

From the foregoing description, it will be seen that the presentinvention provides a thermistor body composition which permits the useof low cost terminal wires without causing undue voltage sensitivity.

It will be understood that the details and examples I hereinbefore setforth are illustrative only and that the invention as broadly describedand claimed is in no way limited thereby.

A semi-conductor comprising a body formed of a re- References Citedinthe file of this patent UNiTED STATES PATENTS 2,329,511 ChristensenSept. 14, 1943 2,407,288 Kleimack et al. Sept. 10, 1946 2,414,793 Beckeret al. Ian. 28, 1947 2,720,573 Lundquist Get. 11, 1956 2,871,197Maclntyre et al. Jan. 27, 1959 2,936,434 1960 Postal May 10,

